The present invention relates to electrical measurements and, in particular, to closed loop measurement systems.
It has become ubiquitous to use feedback loops in measurement systems to ensure that signals (e.g., current, voltage) impressed on a device under test (DUT) are the desired signal and not some approximation caused by such factors as cable losses, stray impedances and interference coupling.
Historically, DC measurements and AC measurements (e.g., LF, pulse and RF) measurements were made separately on a DUT. Increasingly, the market is demanding that these measurements be integrated.
Establishing a known DC bias on a DUT is complicated by the fact that the AC measurement will likely try to make the DC bias “move”. In these cases, the AC loop and the DC loop may “fight” each other. This is particularly the case where it is desired to quickly establish bias levels. By minimizing settling times, measurement throughput can be maximized; however, this increases the likelihood that the DC and AC feedback loops will conflict.